invention relates, generally, to the bridging and dampening systems used in duplicating machines, for example, offset-type presses. As is well-known in the art, the typical offset duplicator includes a master cylinder which carries a master or printing plate having ink receptive image areas and repellant solution or water receptive background areas formed thereon. Ink is transferred to the master by the inking system, and repellant solution is transferred to the master by the dampening system. The ink receptive image on the master plate retains the ink while the non-image areas of the master plate are receptive to the repellant solution and repel the ink.
A blanket cylinder is rotatably engaged with the master cylinder and has a blanket adapted to receive an offset, inked image from the master plate. A rotatable impression cylinder contacts the blanket cylinder such that a sheet of paper can be fed therebetween. As the paper passes between the blanket cylinder and impression cylinder, the latter applies pressure upwardly against the sheet such that the image from the blanket cylinder is transferred to the sheet of paper.
An exemplary dampening system may include a fountain roller, partially immersed in the repellant solution, which contacts and delivers the repellant solution to a metering roller. The metering roller, contacts and delivers the repellant solution to a dampening form roller which, in turn, contacts the master or printing plate on the master cylinder to transfer the repellant solution thereto.
An exemplary inking system may include an ink fountain roller, partially immersed in ink held by an ink fountain, which contacts and transfers ink to an oscillating roller. The oscillating roller reciprocates along its axis of rotation as it rotates to thereby ensure that the ink is evenly spread over the roller's surface. The ink is transferred, through a series of transfer rollers, to inking form rollers which contact the master cylinder to supply ink to the master or printing plate.
Each time the ink passes through the area between the nip of two rollers, it is split such that a portion of the ink adheres to each roller. As is well known in the art, the printing capability of the ink is improved each time it passes through a nip. The splitting of the ink at the nip gives a thinner and more uniformly distributed layer of ink on the rollers and the pressure applied to the ink at the nip by the rotating rollers makes the ink more pliable. Because these inking characteristics result in a higher quality printed product, it is desirable to maximize the number of rollers in the ink path and, therefore, increase the nips through which the ink passes before being applied to the master plate.
One way of maximizing the number of nips in the system is to increase the number of transfer rollers in the inking system. However, due to size constraints the number of rollers that can be included in the ink path is limited. In order to overcome this limitation, the inking system and dampening system can be connected with one another by a bridging system to create what is known in the art as an integrated system. In the integrated system the ink is delivered to the master or plate along a path that includes a portion of the dampening system. Thus, the number of nips through which the ink passes is increased by addition of the rollers to the ink path in the dampening and bridging systems.
While the integration of the inking and dampening systems results in the delivery of a higher quality ink to the master plate, it is desirable at times to run the inking system separately from the dampening system in a, so-called, segregated mode. Typically, the segregated mode is used for very fine line work where a less viscous ink is preferred. Therefore, there is a need for a printer which can be quickly and easily changed over between the integrated and segregated modes.
U.S. Pat. No. 4,676,156 to Aylor et al. shows a known dampening apparatus for an offset printer. The inking supply is shown integrated with the dampening system through a distribution roller. The distribution roller is supported on pivotable brackets such that contact between the distribution roller and the applicator roller of the inking system can be interrupted. A set screw and slot arrangement secures the pivotable brackets and in the desired position.
The bridging system 63 and dampening system 31 of the present invention are shown in association with a known inking system in FIG. 1. When the inking system shown in FIG. 1 is used with the dampening system of Aylor et al., the ink that is transferred directly to the distribution roller will be transferred to the dampening system even in the segregated mode because the distribution roller never breaks contact with the applicator roller of the dampening system. Thus, the Aylor et al. dampening system, when used in conjunction with the inking system shown in FIG. 1, would not operate in a truly segregated mode. Moreover, because some ink would be transferred to the dampening system through the distribution roller and the inking form rollers, and thus would not receive a full supply of ink. An additional drawback of the arrangement shown by Aylor et al. is the time and expertise required to release, fasten, and properly locate the set screws when changing between the integrated and segregated modes. Moreover, specialized tools are necessary to loosen and tighten the set screws. Thus, a more convenient method for changing between the integrated and segregated modes is desired.
West German Patent DE No. 3,641,013 issued to Jentzsch et al. shows a printing machine in which the inking and dampening systems can be selectively integrated and segregated. The inking form roller and dampening form roller can also be selectively engaged or disengaged from the master cyclinder. However, the means for moving the rollers into and out of engagement with one another consists of a complicated system of linkages and a cam/cam follower arrangement. As a result, the system is not adapted for the ease of manual positioning of the rollers as is the case with the present invention. Moreover, such a complicated system requires numerous fine adjustments to accurately position the rollers.
In addition to the ability to be able to change between the integrated and segregated modes, it is also necessary to be able to move the applicator form roller of the dampening system out of contact with the master cylinder so as to be able to remove and replace the master plate. While Aylor and Jentzsch et al. discloses such a capability, the mechanisms for performing this function are cumbersome to operate.
Moreover, the known prior art devices do not provide a simple and effective way to isolate the fountain roller and metering roller from the remainder of the system to allow the metering roller to be prewet with repellant solution prior to transferring ink thereto. As a result, the start up of the printer is complicated by the difficulty of prewetting the metering roller.
Finally, the known prior art devices do not provide a simple and effective way of isolating the inking system and the dampening form roller from the remainder of the system to facilitate the clean up operation. As a result, in the known systems the components must be individually cleaned.